Objective: To evaluate and compare marginal bone loss around mini-implants supporting maxillary overdentures with either partial or full palatal coverage.
Method and Materials: Nineteen edentulous patients complaining of retention problems involving their maxillary dentures were randomly allocated in two groups. Group I (n = 10) received maxillary dentures with full palatal coverage, and group II (n = 9) received maxillary dentures with partial palatal coverage. In total, 114 mini-implants (6 per patient) were inserted using the nonsubmerged flapless surgical approach and loaded immediately with maxillary overdentures. Each implant was evaluated at the time of initial prosthetic loading and at 6, 12, and 24 months thereafter. Radiographic evaluation was performed in terms of vertical and horizontal bone loss. Implant mobility (via Periotest values) was measured using a Periotest device, and patient satisfaction was evaluated with a visual analog scale. The cumulative survival rate was calculated using Kaplan-Meier analysis.
Results: After 2 years, the mean vertical bone loss in groups I and II was 5.38 and 6.29 mm, respectively, while the mean horizontal bone loss in groups I and II was 1.52 and 1.93 mm, respectively. Most bone resorption occurred within 6 months after overdenture insertion in both groups. Group II recorded significant higher vertical bone loss and Periotest values than group I at all observation times. The cumulative survival rates of the mini-implants were 78.4% and 53.8% for groups I and II, respectively. All patients were satisfied with their maxillary overdentures in terms of retention and chewing ability.
Conclusion: Rehabilitation of edentulous maxillae with unsplinted mini-implants supporting overdentures and in particular with a combination of partial palatal coverage is not recommended because of excessive marginal bone resorption and the higher failure rate of mini-implants than was expected.

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